Progress in geodetic techniques allows us to detect “slow earthquake” transients (eg, slow slip events, SSE) by increasing accuracy and range. Recent observations reveal changes in SSE behavior that are interesting before and / or after an earthquake. However, the physics behind this observation remains largely unknown. How do SSE patterns change during the megathrust super-cycle earthquake? What is the SSE response to “external” tectonic disorders such as earthquake stress disorder, or non-tectonic forces such as tide modulation and seasonal loading? Can changes in SSE patterns explain the occurrence of a large earthquake? To answer these questions, we implemented laboratory-based state-and-state friction laws regarding faults in subduction zones with realistic friction properties that combine megathrust earthquakes and SSE regions. We conducted a quasi-dynamic 2D / 3D earthquake cycle simulation to study SSE pattern changes “intrinsic” when it evolved at various stages of the earthquake cycle, compared with changes in SSE patterns that respond to external pressure disturbances. Our results show that, although both intrinsic and perturbation models are able to introduce large variability in SSE patterns, there are many observable characteristics that can be used to distinguish between these two models. Without external interference, the SSE pattern changes intrinsically during the super cycle. The looping interval and SSE peak slip level decreased significantly just before the megathrust earthquake and can be used as a potential warning sign. Whereas SSE patterns can vary greatly when disturbed by earthquakes or other tectonic / non-tectonic sources. Repeated SSE can be forwarded or delayed by external interference, and some SSEs can be affected if the interference is durable.